The present disclosure relates to phosphor compositions, particularly phosphors for use in fluorescent lamps. More particularly, the present disclosure relates to phosphor compositions that can produce white light and include a special BAMn phosphor, (Ba,Sr,Ca)(Mg1-xMnx)Al10O17:Eu2+, where x is defined below, without using BAM phosphor, BaMgAl10O17:Eu2+.
Fluorescent lamps typically have a transparent glass envelope enclosing a sealed discharge space containing an inert gas and mercury vapor. When subjected to a current provided by electrodes, the mercury ionizes to produce radiation having primary UV wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the envelope to produce visible light which is emitted through the glass.
Generally, a fluorescent lamp for illumination uses a phosphor which absorbs the 254 nm Hg-resonance emission wavelength and is activated so as to convert the ultraviolet luminescence of mercury vapor into visible light. In order to improve the color-rendering properties and emission output of fluorescent lamps, a three-band type fluorescent lamp, which employs a mixture of red, green and blue-emitting phosphors, has been used to render illumination of a white color. For example, the phosphor may include a mixture of europium-activated barium magnesium aluminate phosphor (BaMgAl10O17:Eu2+) for the blue-emitting phosphor, cerium- and terbium-coactivated lanthanum phosphate phosphor (LaPO4:Ce3+, Tb3+) for the green-emitting phosphor, and europium-activated yttrium oxide phosphor (Y2O3:Eu3+) for the red-emitting phosphor, mixed in an adequate ratio. The combined spectral output of such a phosphor blend produces a white light.
The apparent color of a light source is described in terms of color temperature, which is the temperature of a black body that emits radiation of about the same chromaticity as the radiation considered. A light source having a color temperature of 3000 Kelvin has a larger red component than a light source having a color temperature of 4100 Kelvin. The color temperature of a lamp using a phosphor blend can be varied by changing the ratio and composition of the phosphors.
Color quality is further described in terms of color rendering, and more particularly color rendering index (CRI or Ra), which is a measure of the degree to which the psycho-physical colors of objects illuminated by a light source conform to those of a reference illuminant for specified conditions. CRI is in effect a measure of how well the spectral distribution of a light source compares with that of an incandescent (blackbody) source, which has a Planckian distribution between the infrared (over 700 nm) and the ultraviolet (under 400 nm). The discrete spectra which characterize phosphor blends will yield good color rendering of objects whose colors match the spectral peaks, but not as good of objects whose colors lie between the spectral peaks.
Color rendition is a measure of the light reflected by a color sample under a given light source, compared to the light reflected by the same sample under a standard light source. Color rendition is calculated as disclosed in “Method of Measuring and Specifying Colour Rendering Properties of Light Sources, 2nd Edition”, International Commission on Illumination, Publication CIE No. 13.2 (TC-3.2) 1974, the contents of which are hereby incorporated by reference. The differences in value, chroma and hue of the light reflected under the two sources are measured and summed, the square root of the sum is taken, multiplied by a constant, and subtracted from 100. This calculation is done for 14 different color standards. The color rendering index for each of these standards is designated Ri. The General Color Rendering Index, Ra, is defined as the average of the first eight indices, R1-R8. The constant has been chosen such that Ra for a standard warm white fluorescent tube is approximately 50. It should be noted that an Ra of 100 corresponds to a light source under which the color samples appear exactly as they would under a standard light source, such as an incandescent (black body) lamp or natural daylight.
The color appearance of a lamp is described by its chromaticity coordinates which can be calculated from the spectral power distribution according to standard methods. See CIE, Method of measuring and specifying color rendering properties of light sources (2nd ed.), Publ. CIE No. 13.2 (TC-3, 2), Bureau Central de la CIE, Paris, 1974. The CIE standard chromaticity diagram includes the color points of black body radiators at various temperatures. The locus of black body chromaticities on the x,y-diagram is known as the Planckian locus. Any emitting source represented by a point on this locus may be specified by a color temperature. A point near but not on this Planckian locus has a correlated color temperature (CCT) because lines can be drawn from such points to intersect the Planckian locus at this color temperature such that all points look to the average human eye as having nearly the same color.
Another parameter with regard to light emission is luminous efficacy of a source of light is the quotient of the total luminous flux emitted by the total lamp power input as expressed in lumens per watt (LPW or lm/W).
Spectral blending studies have shown that the LPW and CRI of white light sources are dependent upon the spectral distribution of the individual color phosphors. It is expected that such phosphors will remain stable during extended lamp operation such that the phosphors remain chemically stable over a period of time while maintaining stable CIE color coordinates of the lamp. The human eye does not have the same sensitivity to all visible light wavelengths. Rather, light with the same intensity but different wavelengths will be perceived as having different luminosity.